High Voltage Forum

Electromagnetic radiation => Light, lasers and optics => Topic started by: MRMILSTAR on September 29, 2019, 05:44:12 AM

Title: Power supply for gas discharge tubes
Post by: MRMILSTAR on September 29, 2019, 05:44:12 AM
I bought several gas discharge tubes at a swap meet recently. They contain various gases such as krypton, helium, argon, and nitrogen. Each tube is made of glass and is about 12 inches long and 0.5 inch wide. There are leads protruding from each end. What is the best way to power these tubes to get good brightness without burning them out? What is a good voltage and current? I have on hand a NST and MOTs. I also have a variac to control the voltage if necessary. I also have various tesla coils but I wanted a power source independent of those.
Title: Re: Power supply for gas discharge tubes
Post by: klugesmith on September 29, 2019, 08:57:03 AM
Ooh, colors!  Do you have any sort of spectrometer, perhaps just a simple prism or diffraction grating?

If they're cold cathode tubes, you can't go wrong with a NST on a variac.  Operating current is determined by the variac setting. If the tubes came as a set, they're probably all OK with the same current, and could be connected in series and lit all together.  For a more compact power supply, I bet an inverter for driving CCFL lamp, such as those in laptop computer displays, would work

The advice would be different (and speculative) if there's a coiled tungsten filament at each tube end, like those in compact fluorescent lamps.  Even if not designed for electrical preheating, I think that kind of cathode wants enough arc current to keep it sort of hot. 

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Title: Re: Power supply for gas discharge tubes
Post by: MRMILSTAR on September 29, 2019, 05:27:23 PM
I looked at the tubes. I see no filament so I assume that they are cold cathode tubes. I bought them as part of a set. Would it be better to connect them in series or in parallel?

I wonder if those E-Bay tubes you show use different gases to achieve the colors or just a filter.

I need to get a prism.
Title: Re: Power supply for gas discharge tubes
Post by: Twospoons on September 29, 2019, 11:31:46 PM
Series, definitely.  In parallel  the first one to strike will prevent the others from lighting up.
Title: Re: Power supply for gas discharge tubes
Post by: davekni on September 30, 2019, 04:58:49 AM
A bit of poking on EBay suggests they are indeed CCFLs, so based on mercury arc with phosphor coating on the inside of the glass, likely designed for 5mA.  The easiest is probably to buy some cheap CCFL drivers.  There are plenty available with 4 outputs for relatively little cost:
    https://www.ebay.com/itm/Inverter-Ballast-for-CCFL-Angel-Eyes-Halo-Rings-Kit-4-outputs-12V-Male-900V/362211813813?hash=item545581a9b5:g:SVgAAOSwM~taWS2F
    https://www.ebay.com/itm/Spare-Inverter-Ballast-for-CCFL-BMW-Angel-Eyes-Halo-Rings-Kit-4-outputs-Female/264317522214?hash=item3d8a8d5126:g:BFoAAOSwt~1c1bcS
for a couple examples.  There are bare boards for laptops and TVs available too